IONIC BOND
Ionic bonding involves the transfer of electrons from an electropositive atom (an atom that tends to "donate" an electron) to an electronegative atom (an atom that tends to "accept" an electron). Ionic bonding allows the atoms to form completely filled (and therefore stable) valance shells. The transfer of electron results in a positively charged ion and negatively charged ions. Which are drawn to each other by columbic attraction until their filled electron shells overlapped? A high difference between the electro negatively of two atoms increases their tendency to form an ionic bond. Generally, the electro negatively of two atoms increases from left to right of the periodic table. Table salt, or NaCl, is an example of a compound with ionic bonding between an electropositive element (Na) and an electro negative atom (Cl). Chlorine has 17 total electrons: 2 in its first shell, 8 in the 2 shell, and 7 in the 3. We know that the capacity of the 3 shell is 8, so chlorine will try to pick up another electron to fill its outermost shell. Where does it get this electron? For some atoms it is easier to loss electrons than to pick up new ones. Sodium to have a full valance shell it can do one of 2 things: pick up 7 new electrons (which is very difficult thing to do) or give up one. If sodium gave up the one electron in its 3 shell, this shell will now be empty and the second shell (which is filled with 8 electrons) would becomes its valance shell. Thus chlorine and sodium is a perfect match for each other. One needs an electron and other wants to lose an electron. When this transfer takes place, sodium looses an electron and become positively charged, so after losing an electron sodium will have one more positively charged proton than it does negatively charged electrons. And since chlorine gains an electron it becomes negatively charged. In this way both atoms now become ions. The positive charge on the Na+ and Cl- ions will cause them to attract each other and form an ionic bond.